The present invention relates to devices for controlling the introduction of fuel tank vapor into the air inlet of an internal combustion engine to prevent escape of the fuel tank vapors into the atmosphere. Recently legislated standards for the amount of permissible fuel vapor emissions from unburned fuel have required the complete closure of engine fuel supply systems utilizing volatile fuel.
In particular, the legislated standards for controlling the emission of unburned engine fuel in motor vehicles has required that the fuel vapor be stored and contained during periods of engine inoperation and the storage vessel purged during engine operation. In typical motor vehicle systems, a carbon filled canister adsorbs the fuel vapors during periods of engine inoperation and the canister is purged by allowing the fuel vapors in the canister to enter the engine air intake or intake manifold during engine operation.
However, it is necessary to control the flow of such stored fuel vapor to the engine intake manifold in order to prevent overly rich combustion in the engine which would in turn produce unacceptable emissions of products of the engine combustion or rough engine operation and stalling.
Currently, motor vehicles, particularly light trucks and passenger vehicles employ electrically operated fuel injectors which are controlled by an electronic control unit (ECU) which receives signals from sensors measuring the engine operating parameters, including the chemical composition of the engine exhaust. It has thus been desired to incorporate control of the fuel vapor purge with the electronic control of the engine via the ECU.
In earlier fuel vapor purge systems, a solenoid operated valve Controlled atmospheric bleed to a vacuum signal from the engine intake manifold to provide a reference pressure for a pressure regulator valve. This technique has the drawback of creating an atmospheric vent flow to the intake manifold and vacuum loss in the manifold.
More recently it has been proposed to control the flow from the vapor canister to the engine intake manifold by means of a pressure regulator with a solenoid operated valve controlling vapor flow from the canister to the inlet of the pressure regulator in response to a control signal from the ECU. Such a device and control technique is shown and described in the co-pending application of Daniel DeLand and Charles Detweiler entitled "Fuel Vapor Purge Control", Ser. No. 08/949,106, Filed Oct. 10, 1997 and assigned to the assignee of the present invention. The latter device utilizes an elastomeric diaphragm for operating the pressure regulator valve and has the solenoid operated valve attached to the regulator body and the solenoid operated valve is potted to control flow around the diaphragm. Typically, diaphragm operated pressure regulator valves are constructed in a manner so as to have the diaphragm periphery exposed to the atmosphere. In such constructions, where the diaphragm is formed of materials suitable for the extremes of temperature encountered in vehicle service, problems have been encountered with migration of the fuel vapor to the edges and evaporation to the atmosphere.
In addition, the aforesaid type fuel vapor purge control valve assemblies have required a separate in-line filter between the regulator valve assembly and the fuel canister to prevent carbon particles from the canister and other foreign material from entering the regulator valve and causing malfunction of the valve such as by valve seat contamination.
Accordingly, it has been desired to provide an electrically controlled pressure regulating fuel vapor purge control valve which is sealed sufficiently to prevent migration and escape of fuel vapor to the atmosphere, through the diaphragm is resistant to entrance and entrapment of foreign particles, is easy to assemble and calibrate, reliable in extended service, and is low in manufacturing costs.